High impact withstanding taut band suspension instrument

ABSTRACT

In a taut band suspension instrument in which each taut band extends between two convex support surfaces and the end portions of the taut band are secured to the respective supports by fused metal connections at points spaced radially from the axis defined by the band, the support surface at the end of the band farther from the rotor is provided with a shallow groove, the bottom of the groove being continuous and uninterrupted and having a width at least twice the width of the taut band, the support surface at the other end of the band being smooth and unbroken for the full width thereof. The combination of the two support surfaces allows the taut band to shift laterally when the instrument is under shock, yet assures that the outer end of the taut band will be properly oriented when installed and thereafter.

rite States Patent ii oreas 51 July 18, 1972 [72] Inventor: Willem J. L.Boreas, Sayreville, NJ. [73] Assignee: Weston Instruments, Inc., Newark,NJ.

[22] Filed: May 3, 1971 [21] App]. No.: 139,513

Related U.S. Application Data [63] Continuation-impart of Ser. No.836,828, June 26,

1969, Pat. No. 3,624,505.

Primary Examiner-Alfred E. Smith Attorney-William R. Sherman, Jerry M.Presson' and Roylance, Abrams, Berdo & Kaul [57] ABSTRACT In a taut bandsuspension instrument in which each taut band extends between two convexsupport surfaces and the end portions of the taut band are secured tothe respective supports by fused metal connections at points spacedradially from the axis defined by the band, the support surface at theend of the band farther from the rotor is provided with a shallowgroove, the bottom of the groove being continuous and uninterrupted andhaving a width at least twice the width of the taut band, the supportsurface at the other end of the band being smooth and unbroken for thefull width thereof. The combination of the two support surfaces allowsthe taut band to shift laterally when the instrument is under shock, yetassures that the outer end of the taut band will be properly orientedwhen installed and thereafter.

8 Claims, 12 Drawing Figures PATENTEU JUL 1 8 I972 sum 2 or 3 FIG. 6

FIG. 8

FIG. 11

FIG. 7

I820 85 82 IBIO INVENTOR WILLIAM J. L. BOREAS PATENTED JUL] 8 I972 sum 3or 3 INVENTOR WILLIAM J. L. BOREAS HIGH IMPACT WITI'ISTANDING TAUT BANDSUSPENSION INSTRUMENT RELATED APPLICATION BACKGROUND OF THE INVENTIONWhile taut band suspension instruments have long been known, suchinstruments have had relatively little capability of withstanding shock.This deficiency has been largely overcome by the construction disclosedin my application Ser. No. 836,828, in which the taut band has a limitedfreedom of lateral movement, relative to its supports, under conditionsof impact. In that construction, the taut band is supported by an innerconnector member, secured to the rotor, and an outer member, secured toa frame or like support, each connector member having a convex supportsurface so disposed that the axis of curvature thereof extendssubstantially at right angles to the axis of rotation of the rotor. Theend portions of the taut band extend across the convex support surfacesand thence to a point of attachment spaced radially from the axis ofrotation. The support surfaces are smooth and uninterrupted and of suchwidth that the taut band can move through a significant distancelaterally while still in contact with, or at least disposed for contactwith, the support surfaces.

The construction further includes stop means so arranged as to limitmovement of the rotor, and therefore the inner connector members carriedthereby, axially relative to the frame and also to limit movement of theouter connector members axially away from the inner connector members,the stop means being such that the outer connector members are limitedto an outward travel smaller than the axial distance through which therotor is allowed to move. The inner connec tor members are in the formof stiff arms, and the outer connector members are resilient.

Connection of the taut bands to the inner connector members can beaccomplished with the aid of a jig which assures that the band willextend substantially precisely across the center of the convex surfacepresented by the inner connector member. Connections of the bands to theouter connector members, however, must be made manually, without the useof a jig. Considering that the band is, advantageously, on the order of0.005 in. wide and 0.0003-0.0004 in. thick, it will be understood thatprecise positioning of the band on the outer connector member isdifficult to achieve manually. And the results of improper positioningof the band relative to the outer connector member can be significantlydeleterious. For example, if the band is inadvertently offset from thecenter of the convex support surface presented by the outer connectormember by several thousandths of an inch and the adjacent end portion ofthe band is, e.g., welded to the outer connector member with theinadvertent offset existing, the weld retains the end portion of theband in a normal position which is angularly offset by several degreesfrom the desired radial center of the outer connector member. Suchangular offset not only improperly locates the taut band relative to theconvex support surface but also causes an excessive stress concentrationin the band at the weld, so that the ability of the taut band in theassembled instrument to withstand high impacts may be reduced.

OBJECTS OF THE INVENTION A general object of the invention is to providea taut band suspension system, of the type described, in which precisecentering of the band relative to the convex support surface of theouter connector member is achieved without loss of the capability ofwithstanding high impacts which stems from the freedom of lateralmovement which the band is allowed.

Another object is to provide, in such a suspension system, lateralrestrictions on movement of the taut band which are effective to assureproper positioning of the band during assembly and when the band isfully taut but which do not impede extreme lateral shifting of the bandrelative to the outer connector member under the slackened condition ofthe band encountered when the instrument is subjected to a high impact.

SUMMARY OF THE INVENTION Considered broadly, taut band suspensionsystems according to the invention include an outer connector member,advantageously in the form of a resilient arm, presenting the desiredconvex supporting surface for the taut band, the supporting surfacebeing smooth and unbroken but being disposed between two raised portionswhich extend generally in the direction of the length of the band. Thus,the portion of the outer connector member which presents the convexsupporting surface over which the band extends can be considered ashaving a shallow, relatively wide groove, with the supporting surfaceconstituting the transversely fiat bottom of the groove and being atleast twice as wide as is the band, the sides of the groove constitutingraised portions having a height at least approximately equal to thethickness of the band. During assembly, the appropriate end portion ofthe band is manipulated manually to extend between the raised portions,along the length of the connector member, and through a locator notchand, with the band held in that position, the band is secured to theconnector member by a fused metal joint, advantageously a spot weld,which is distant from the convex supporting surface and fixes a portionof the length of the band which is greater than the width of the band,so that the joint tends to constrain the band to its centered positionon the convex support surface.

In order that the manner in which the foregoing and other objects areachieved according to the invention can be understood in detail, oneparticularly advantageous embodiment thereof will be described withreference to the accompanying drawings, which form a part of theoriginal disclosure of this application, and wherein:

FIG. 1 is a front elevational view of an electrical meter according tothe invention;

FIG. 2 is a longitudinal sectional view taken generally on line 2-2,FIG. 1, and being on larger scale than is FIG. 1;

FIGS. 3 and 4 are transverse sectional views taken generally on lines3-3 and 4-4, respectively, FIG. 2;

FIG. 5 is a view, partly in longitudinal cross section and partly inside elevation, of a taut band and its associated connector members,forming part of the meter of FIGS. l4;

FIG. 5A is a fragmentary view showing the outer connector member of FIG.5 with the taut band in a position resulting from high impact on themeter;

FIG. 6 is an end elevational view of the combination shown in FIG. 5;

FIG. 7 is a view taken generally on line 7-7, FIG. 5;

FIG. 8 is a transverse sectional view taken generally on line 8-8, FIG.5;

FIG. 9 is a perspective view of the combination of elements shown inFIG. 5; and

FIGS. 10 and 11 are sectional views similar to FIG. 8 but showing theouter connector member in modified form.

Referring now to the drawings in detail, and particularly to FIGS. 1 and2, there is shown an instrument in the form of a permanent magnet movingcoil meter 1 which is provided with the improved taut band suspensionarrangement of this invention. Meter 1 includes a stationary assembly inthe form of a support frame 2, and a movable assembly in the form of acoil assembly 3 supported for pivotal movement by frame 2.

Frame assembly 2 includes a front frame element 4 and a rear frameelement 5 which are secured to a magnetic structure 6 of the meter. Themagnetic structure 6 includes a ring 7 of magnetic material and acylindrical permanent magnet core 8 within the ring. The core is of asmaller diameter than the inside surface of the ring to provide theusual annular air gap 9 between the ring and the core.

Core 8 is maintained in concentric relation to the ring by spacer blocks10 and 11 which are of nonmagnetic material and extend through air gap 9in diametrically opposed relation to each other and are securedrespectively to the core and the ring. The magnetic structure 6 isdisposed between front frame element 4 and rear frame element 5 and theframe elements are securely clamped to the ring 7 of the magneticstructure by screws 13 which extend between the respective frameelements.

Coil assembly 3 includes a coil 14 having a plurality of turns ofinsulated coil wire wound on a rigid rectangular coil form 15. As shownat FIG. 2, the internal dimensions of the coil form 15 are only slightlygreater than the external dimensions of core 8 and hence all the insidesurfaces of the coil form are spaced slightly from the exterior surfacesof the core. The coil assembly is, of course, positioned on the corebefore the core is secured to ring 7.

The coil assembly 3 also includes a hub 16 secured to one side of coilform 15 and a hub 17 secured to the opposite side of coil form 15 andaligned with hub 16. Each hub has a threaded cylindrical tip 18 and theaxes of the tips are aligned with each other and pass through thegeometric center of coil form 15. Each hub also has a cylindricalportion 19, slightly larger than the tip, and with flat sides 20.Cylindrical portion 19 terminates at a transverse annular shoulder 21.Spaced inwardly of shoulder 21, in a direction toward coil 14, is asecond shoulder 22. Between these shoulders is a cylindrical portion 23which extends between the transverse surfaces of the shoulders Each hubhas a central bore 24 and a transverse slot 25 which extends from thefront of tip 18 to a location slightly inwardly of shoulder 22 toprovide a flat outwardly facing surface 26.

Mounted on hub 16 is an inner connector member 28 which is ring-shapedand has a radially inwardly projecting arm 29 which extends through slot25. The inside diameter of the ring-shaped portion of connector member28 corresponds with the outside diameter of cylindrical portion 23 sothe connector member is snugly received on cylindrical portion 23 of thehub and the inner face of the connector seats on shoulder 22. A pointer30 is mounted on cylindrical portion 19 of hub 16. The pointer has anopening with flat sides that engage the flat sides 20 (FIG. 3) so thepointer is mounted on the hub against rotation. A nut 31, threaded ontotip 18, engages the front face of pointer 30 and holds the pointeragainst shoulder 21 of the hub. The thickness of connector member 28 isslightly greater than the distance between shoulders 21 and 22 so theconnector member is held against axial movement relative to the hub.

Hub 17 is substantially identical to hub 16. Mounted on hub 17 is aninner connector member 32 identical to connector member 28. Connectormember 32 has a ring-shaped body that extends around cylindrical portion23 of hub 17 and a radially inwardly projecting arm 33 that extendsthrough slot 25. The inner face of member 32 engages shoulder 22 of thehub. A counterweight 34 with an opening therein having flat sidescorresponding to sides 20 of cylindrical portion 19 extends over thecylindrical portion and seats against shoulder 21 (FIG. 2). The flatsides prevent rotation of the counterweight relative to hub 19. A nut 35identical to nut 31 is threaded onto tip 18 of hub 17 to hold thecounterweight and connector member 32 against endwise movement.

Formed in front frame element 4 is a cylindrical bore 36. Extendingthrough bore 36 is a molded bushing 37 formed from a semirigidthermoplastic material with good electrical insulating properties, suchas polyethylene or polytetratluoroethylene. Bushing 37 has afrusto-conical inner end 38 which extends outwardly of cylindrical body39 and terminates at a transverse shoulder 39'. Shoulder 39' engages theinner surface 40 of front frame element 4 to prevent movement of thebushing in a direction away from coil assembly 3.

End 38 is transversely split so it can be inserted through bore 36.Bushing 37 also has an enlarged head 41 with a transverse annularsurface 41 that faces toward shoulder 39. The front face 42 of head 41is cut at an angle along one side as at 42'. Formed in front face 42 isa rectangular slot 43 which extends from one side of the head to theother and follows the contour of face 42.

Mounted on cylindrical body 39 of bushing 37 is a zero setting oradjusting arm 44 having its outer surface in engagement with surface 41.Arm 44 is secured to the bushing, advantageously, with an epoxy cement,so the arm is fixed against movement relative to the bushing. Positionedon body 39 adjacent arm 44 is a flat washer 45. A Belleville type springwasher 46 is positioned on body 49 between outer surface 47 offrontframe element 4 and the flat inner face ofa washer 45. It will beobserved with references to FIG. 2 that the body 39 of bushing 37 ismounted for rotation in opening 36 of frame element 4 and that shoulder39' of the bushing is biased into engagement with inner surface of theframe element by the action of the Belleville spring 46.

As shown at FIG. 4, a pair of spaced apart pins 48, formed integrallywith bushing 37, project outwardly from the front face 42 of thebushing. An outer connector member 49 of generally U-shapedconfiguration, having a radially inwardly projecting arm 80, is providedwith openings 51 (FIG. 4) to receive the pins 48. Connector member 49 issandwiched between a front end member 52 and the front face 42 ofbushing 37. As shown at FIGS. 1 and 4, the pins 48 project throughopenings in member 52 and extend beyond the front face 53 ofthe member.The member 52 and connector member 49 are connected to the bushingagainst rotational, as well as axial, movement by deforming the portionsof the pins which extend through member 52 with a heated instrument sothe tips of the pins are deformed as at 54, over front face 53.

Bushing 55 at the opposite end of the meter is identical to bushing 37and extends through a cylindrical opening 56 in rear frame element 5.Bushing 55 has a transversely split tapered end 57 terminating at atransverse shoulder 58, which engages the inner surface 59 of the rearframe element 5. The head 60 of the bushing is identical to head 41,previously explained, and has a bevelled side 61, and a rectangular slot62 formed in the end face 63 of the bushing. A Belleville type springwasher 64 is mounted on the bushing and engages the outside face 65 offrame element 5, and also engages one face ofa washer 66. A spacerwasher 67 engages the transverse surface 68 of head 58. Secured to theouter end of the bushing is a second outer connector member 69 identicalto connector member 49, and an end member 70 identical to end member 52.End member 70 and connector member 69 are secured to bushing 55 in thesame manner as explained for end member 53 and connector member 49.

As seen in FIG. 3, connector member 28 has a flat ringshaped body 71,and arm 29 projects radially inwardly from the body. Body 71 is enlargedtransversely, along the length of arm 29, to provide an outwardlyextending lug 72. This outwardly extending lug 72 permits securing thetaut band ele ment to connector member 28 at a location spacedsubstantially from the axis of rotation of coil 14, in a manner whichwill be explained in detail. As shown at FIG. 2, connector member 28 hasa thickness which is substantially greater than the thickness of outerconnector member 49 so the arm 29 is rigid. The inner end of rigid arm29 is curved through an angle of approximately so it presents a convexsurface 73 which merges smoothly into the transverse surface 74 alongthe length of arm 29.

Connector member 32 is identical to member 28, including arm 33, lug 75,and the rounded end on arm 33 which presents a convex surface 76, therounded end of arm 33 being directed away from coil assembly 3 in thecompleted meter. Like connector member 28, member 32 is of relativelythick sheet metal so as to be essentially rigid with respect to forcesapplied to arm 33 by the taut band.

The body of connector member 49 is generally U-shaped, includingsupporting legs 78 and 79 which lie flush against the front face 42 ofbushing 37. Member 49 includes an arm 80 which is connected to legs 78and 79 via relatively thin portions 81 between the respective legs andthe arm. Member 49 is formed from thin sheet spring material, such asphosphor bronze, so that arm 80 is resilient and, in the assembleddevice, can flex toward and away from the coil 14.

Arm 80 has a rounded tip 180, FIGS. 5-7, which curves through an angleof approximately 150 and, in the assembled device, extends toward coil14. The side edges of tip 180 are deformed to provide raised portions181 and 182 which are of arcuate transverse cross section. Betweenraised portions 181 and 182, tip 180 presents a convex surface 82 whichmerges smoothly with the transverse surface 83 presented by the outerface of arm 80. Convex surface 82 is transversely flat, so that raisedportions 181 and 182 coact with surface 82 to define a shallow groovewith surface 82 forming the bottom of the groove. Raised portions 181and 182 are convex when viewed toward surface 182 and extend for most ofthe length of the curved tip 180. Raised portions 181 and 182 have amaximum height midway between the ends of curved tip 180, Le, at thecrest of convex surface 181, and taper to a zero height at each end ofthe raised portion.

Connecting portions 81 of member 49 extend circularly through an arewhich is concentric with the longitudinal axis of bushing 37. Arm 80extends radially inwardly, its center line passing through thelongitudinal axis of bushing 37. The length of arm 80 is such that, inthe assembled device, the longitudinal axis of bushing 37 issubstantially tangent to convex surface 82. Opposite tip 180, arm 80 isprovided with a notch 183, FIGS. 4-7, which lies on the center line ofarm 80.

Connector member 69 is identical to connector member 49, and includes aresilient arm 80' identical with arm 80 of member 49. Arm 80 is providedwith raised portions corresponding precisely to raised portions 181 and182 of arm 80.

A first taut band suspension element 85 of elongated rectangulartransverse cross section extends between outer connector member 49 andinner connector member 28. As shown at FIG. 5, suspension element 85 hasa first portion 86 which extends along transverse surface 74 ofconnector member 29, and across convex surface 73 of that connectormember. One wide face of the band engages these surfaces. Suspensionelement 85 also includes a second portion 87 which extends alongtransverse surface 83 of arm 80 and across the convex surface 82 of thisarm. Extending between the portions 86 and 87 is an intermediate portion88. As seen in FIG. 3, portion 86 of band 85 is secured to connectorelement 28 at lug 72 by a relatively small spot weld 89. Similarly, asshown in FIGS. 4 and 6, portion 87 of band 85 is secured to arm 80adjacent the outer end of the arm by a spot weld 90.

In a similar manner, a second taut band 91 (FIG. 2), identi cal to band85, is connected between inner connector member 32 and outer connectormember 69, at the rear of the meter.

As seen in FIG. 2, with connector member 29 positioned on hub 16,connector member 49 positioned on bushing 37, and with connector members33 and 69 similarly positioned at the other end of the meter, coilassembly 3 is suspended by taut bands 85 and 91 for pivotal movementabout the axis determined by these bands. After bands 85 and 91 areinitially tensioned, they are maintained under sufficient tension by theresilient arms of connector elements 49 and 69 so the axis of rotationof the coil assembly is essentially the same regardless of theorientation of the meter.

As previously explained, both bushing 37 and bushing 55 are free torotate in the respective frame elements 4 and 5. Such freedom ofrotation permits adjusting the torsion in the taut bands 85 and 90,after the meter is assembled, so the restoring force from the bands toreturn coil assembly 3 and pointer 30 to zero position can be setprecisely by rotating bushing 37 and 55. After the initial adjustment ofbushing 55, this bushing is secured to frame element 5 against rotationwith a suitable cement. Thereafter, the zero set, for each use of themeter, can be provided by rotating bushing 37 via adjusting arm 44.

Nut 31 hub 16 extends into the central cylindrical opening 93 of bushing13 and nut 31 of hub 17 extends into the bore 94 of bushing 55. It willbe observed with reference to FIG. 2 that there is only a slightclearance between the external surface 95 of the nut on hub 16 andinternal surface 93, and that, similarly, there is only a slightclearance between external surface 96 of the nut on hub 17 and internalsurface 94. Surfaces 93 and 95 function as stop surfaces to limittransverse movement of the coil assembly.

Axial movement of coil assembly 3, in the-event of impact, is limited inone direction by engagement of inside front surface 97 of coil form 15with front surface 98 of core 8, and in the opposite direction byengagement of the rear inside surface 99 of the coil form 15 with rearsurface 100 of the core.

As previously explained, arm of connector member 49 is resilient. Asshown at FIG. 1, end member 52 has inwardly projecting tabs 101 whichextend across the transverse surface 83 of the arm. As shown at FIG. 2,the inside surface 102 of tabs 101 is normally spaced slightly outwardlyfrom arm 80. However, in the event of substantial shock or impact,surfaces 102 function as stop surfaces which are engaged by transversesurface 83 of the arm to limit the extent of deflection of arm 80 in adirection away from coil assembly 3. Stop surfaces 104, on the innersurface of the end member 70, similarly cooperate with arm 80' to limitits deflection in a direction away from the coil assembly 3, as a resultof shock or impact. Advantageously, the stop surfaces 102 and 104 are sospaced from the arms that the maximum deflection of each arm away fromthe coil is less than the distance the coil assembly 3 can move axiallyfrom its normal position, before it engages one of the stop surfaces 98,100 of the core.

The convex surface 73 of arm 29, while curved in front elevational asshown at FIG. 5, is substantially flat in a direction perpendicular tothe side edge of portion 86 of the band and is substantially wider thanthe band. Hence, convex surface 73 takes the form of the surfacegenerated by a straight line moved along the curvature of the surface ina direction perpendicular to the length of the line. While the convexsurface does have some characteristics of a cylindrical surface, thisconvex surface need not be truly cylindrical. Since convex surface 73includes any of a number of lines parallel to each other andperpendicular to the edge of portion 86 of the band, convex surface 73will be termed transversely flat. Surface 73 extends completely to theedges of the tip of arm 29, this arm having no elements corresponding toraised portions 181, 182 of arm 80.

The convex surface 82 of connector member 49 is similarly transverselyflat and of a width substantially greater than the width of taut band85. Like surface 73, convex surface 82 takes the form of a surfacegenerated by a straight line moved perpendicular to its axis along thecurvature of the convex surface.

Band is formed from a ribbon of a suitable alloy having a width from 8to 12 times its thickness. While in the meter of this invention, bands85 and 91 are each 4 mils wide and 0.4 mils thick, bands 4 mils wide by0.3 mils thick, as well as bands 4 mils wide by 0.5 mils thick can alsobe used to advantage. Since the band has substantial width as comparedto its thickness, stresses are established in the side edges of the bandas a result of attempting to pivot the band transversely about the weldspots 89 and 90. However, it has been found that the bands will curveelastically like a beam in response to a force applied to a side edge ofthe band, as when the band moves transversely and attempts to pivotabout the weld point. Correspondingly, the portion 86 and 87 of thebands which extend along the respective arms 29 and 80 will curve alongtheir length about a long radius if a band is displaced from its normalcentral position on the arms, without creating excessive stress in theband at the weld points 89 and 90. However, such elastic curvature withthe absence of stress at the weld points can be obtained only if asubstantial length of the band exlO I045 0447 tends along each arm. Ithas been found that remarkable resistance to breakage of the band in theevent of severe impact is obtained if the convex surface, at the tangentpoint with the intermediate portion 88 of the band, is sufficiently widethat the band can move through an angle of l ll8 about the weld pointwhere the band is fixed to the arm. It has also been found that a band 4mils wide and 04 mils thick will curve elastically transversely of itslength about the weld point, if the length of the band between the weldpoint and the tangent point with the convex surface is at least 50 milsand if the movement of the band from its neutral or central positiondoes not exceed 6 in either direction when the band is in engagementwith the respective arm 29, 80.

In assembling the meter, the end of portion 86 of band 85 is secured toarm 29 by spot welding at 89 after assembling the band and member 28 ina jig (not shown) arranged to assure that end portion 86 extends alongthe center line of arm 29. Assembly is then continued until both member28, with the band now welded thereto, and member 49 are in place.Manipulating the band 85 manually, as with tweezers, end portion 87 ofthe band is then stretched over the middle of the convex surface 82,thence over surface 83, and through notch 183. Presence of raisedportions 181, 182 allows the operator to properly position the band onsurface 82 by eye, and use of notch 183 assures that the band portion 87will extend along the center line of arm 80. Spot weld 90 is thenestablished. Band 91 is installed in identical fashion.

Spot welds 89 and 90 are made with electrodes having a tip diameterwhich is significantly larger than the width of the band. Thus, with aband having a width of 0.004 in. the tip diameter of the weldingelectrode can be 0.01 in., so that the finished weld has a dimension, inthe direction of the length of the band, 2.5 times the width of theband. With a significant portion of the length of the band thus rigidlyfixed to the arm by the fused metal of the weld, the weld tends toconstrain the band to a centered position relative to the arm, even whenthe band is not completely taut. In this connection, the elongatedrectangular transverse cross section of the band tends to cause the bandto behave as a beam, resisting bending in the direction of its width.

The width of surface 82 (and of the corresponding surface of arm 80') isfrom 1.5 to 4 times the width of the band. Typically, with band 85having a width of 0.004 in., the lateral spacing between raised portions181 and 182 can be 0.008 in. With the width of surface 82 then being0.008 in., and with the band 85 centered between raised portions 181 and182, the band can shift laterally over surface 82 through a distance of0.002 in., or half of its width, in either direction. With the width ofsurface 82, as defined by the space between raised portions 181 and 182,being 1.5 to 4 times the width of the band, the band is allowed to movelaterally in either direction over the convex supporting surface of theouter connector member when engaged therewith, through a distance whichis 25-150 percent ofthe width ofthe band.

Raised portions 181 and 182 have a maximum height adequate to bothvisually define surface 82, for the operator who assembles the meter,and laterally restrain the band to surface 82 during assembly. Underconditions of extreme impact on the meter, however, the height ofportions 181 and 182 is adequately small, as seen in FIG. A, to allowthe band, rendered slack by the impact, to move laterally withoutengaging the raised portions. Accordingly, raised portions 181 and 182can advantageously have a maximum height of l-l0 times the thicknessofthe band.

RESISTANCE OF THE SUSPENSION SYSTEM TO IMPACT What is believed to occurwhen meter 1 is subjected to impact, and What is believed to preventbreakage of the fragile bands when used in the taut band suspensionsystem of this invention, will now be explained. First, consider whathappens when the meter is dropped so it lands on a surface adjacent itsend member 70 with the axis of rotation of the coil vertical. At themoment of impact, support assembly 2 will immediately stop, but coilassembly 15 will continue to move until its stop surface 97 engages thefront face 98 of core 8. Such axial movement of coil assembly 3 ispermitted by resilient arm of connector member 49. At the instant ofimpact, the arm 80, because of its mass, will deflect toward coilassembly 3. The arm 80, however, can deflect a greater distance towardcoil as sembly 3, than coil assembly 3 can move axially before itengages the stop surface 98 of core 8. Hence, band is relaxed. At theopposite end of the meter, at the moment of impact, connector member 32moves with the coil assembly toward end member 70. The resilient arm 80'of connector element 69 deflects in a direction away from the coilassembly 3, but its movement is limited by engagement with stop surface104 and is less than the movement of the coil assembly. Hence. at theinstant ofimpact, taut band 91 is also relaxed.

Immediately after impact, resilient arm 80 will spring back and tensionband 85 to pull coil assembly 3 back to its properly suspended position.While there may be some vibration, the coil assembly will ultimatelyreturn to its normal suspended position between the connector members 49and 69. If the shock or impact is applied squarely to end member 70,there will be no transverse forces acting on either band, and hence,even though both bands 85 and 91 were substantially relaxed at theinstant of impact, the band will return to approximately a centralposition on the convex surfaces of the several connector elements, thefact that the band is of elongated rectangular transverse cross sectionand that the spot welds, being significantly elongated lengthwise of thebands, serving as a bias or constraint toward centered position.

Now consider the movement of the coil assembly and bands when the meteris dropped so its axis is horizontal. Assume for purposes of thisexplanation that arm 29 and arm 80 are in the same radial plane, asshown at FIG. 9, and that these arms are vertical at the instant ofimpact. At the instant of impact, frame assembly 2 will stop, but coilassembly 3 will continue to move in a direction perpendicular to itsaxis until the outside surface of the nut on hub 16 engages the insidestop surface 93 of bushing 37, and the outside surface 96 engages theinside surface 94 of bushing 55. At the instant ofimpact, theintermediate portion of band 85, because of its inertia, may deflectdownwardly, but because of the smooth convex surfaces 73 and 82, thereis no stress concentration along the length of the band. Along portions86 and 87 of the band which extend around the convex surfaces and alongthe smooth transverse surfaces of the respective arms, it is believedthat there is sufficient friction to prevent stress concentration in thebands at the weld points 89 and 90.

Now consider the action of the suspension system to resist breakage ofthe taut bands when the arms 29 and 80 are radially aligned, the meteris dropped, and the arms are horizontal at the moment of impact. At theinstant of impact, frame assembly 2 will stop instantly, but coilassembly 3 will continue to move until the surfaces 95 and 96 of nuts 31engage the respective stop surfaces 93 and 94 of bushings 37 and 55. Theeffect of such movement of the coil assembly is to displace member 28from its normal position. Thus, there is some relative movement betweenconnector member 28 and connector member 49, with the result that thetension in band 85 may increase slightly as a result of this movement.In addition, band 85, by virtue of its own inertia, will tend tocontinue to move. Because portion 86 of the band extends along theconvex surface 73 and the smooth transverse surface 74 of connectormember 28, and because the portion 86 of the band is sufficiently longthat it can curve elastically along its length, the portion 86 will movelaterally along convex surface 73 and transverse surface 74 to a gentlycurved position, but such movement will not create stress concentrationsat weld point 89 sufficient to cause failure of the band. Likewise,portion 87 of the band will move along convex surface 82 and smoothtransverse surface 83 of arm 80 and will also curve transversely, butwill not break at weld point 90. As previously stated, a

convex surface on the arms of sufiicient width for the band to swing 1l-l 8 relative to the weld point, where the length of the band extendingaround the convex surface and along the transverse surface of the armsis 50 mils long and has a width of 4 mils, exhibits excellent resistanceto failure. As previously explained, convex surfaces 73 and 82 aretransversely fiat. Hence, any movement of band 85 transversely resultsin an increase in the length of the band with a corresponding increasein the tension in the band. As the tension in the band increases, aresisting force is developed which tends to return the band to itscentral position against the action of the forces I created by shock orimpact. After the impact, the band will tend to return to its originalcentered position, but because of the friction between the length ofportions 86 and 87 of the band, and the corresponding surfaces of thearms 29 and 80, the band may not return precisely to its originalposition. While a small displacement of the band may result, and mayalso occur with band 90, and will affect the accuracy of the instrument,because the axis of the coil assembly 3 is correspondingly displaced, ithas been found that the extent of deviation in accuracy is less than 39% percent of full scale and that the bands did not fail when the meterwas subjected to severe impact with decelerations on the order of 7,000Gs. While ability to withstand very high impact forces is attained byincreasing the length of the band between the weld point and the convexsurface tangent point to, e.g., 50 mils, shorter lengths can beemployed, with a corresponding decrease in impact resistance andincrease in repeatability.

It will be appreciated that connector arms 29 and 80 will not usually beradially aligned with each other at the instant of impact of the meter,because the relationship between these arms depends on the angularposition of coil assembly 3. However, where the arms are aligned in ahorizontal plane at the moment of impact, as explained with reference toFIG. 6, the most severe stresses that can be experienced are exerted onthe bands at the weld points 89 and 90. Such impact tends to cause thebands to fail by bending at the edge of the weld. It will beappreciated, however, that the two arms which support a particular bandmay have virtually any angular relationship to each other and that thestresses in the bands at impact will be substantially less when the armsare displaced angularly than when the arms are aligned. It is alsounlikely that the meter will ever be dropped so it lands with its axisprecisely horizontal or with its axis precisely vertical as in thepreviously explained examples. Hence, the action of the suspensionsystem in avoiding damage to the taut bands is believed to be the resultof a combination of the actions explained above.

In considering lateral movement of the bands relative to theirrespective supporting arms, it is to be noted that raised portions 181and 182 are provided only on the outer connector members 49 and 69 andnot on the inner connector members 28 and 32. Thus, the convexsupporting surfaces presented by the arms of the inner connector memberspresent no impediment to lateral movement of the taut bands and,therefore, allow a greater freedom of lateral movement of the bands thanis allowed, under taut conditions, by the support surfaces and raisedportions 181, 182 of the outer connector members. In effect, presence ofraised portions 181 and 182 on the outer members 49 and 69 is allowablebecause the taut bands can pivot generally in the plane of the lateralmovement, so that the lateral excursion of the bands at the outerconnector members need not be as great as that which is required at theinner ends of the bands to avoid breakage of the bands.

MODIFIED FORMS OF ARMS 80 AND 80' While the configuration of raisedportions 181 and 182, FIGS. 4-9, is particularly advantageous, the tipsof outer connector arms 80 and 80 can be modified considerably. Thus, asshown in FIG. 10, the edges of tip portion 180 can simply be turned upto provide raised portions 181a and 182:: generally in the nature ofside flanges. Alternatively, tip portion 180 can Ill be kept completelyflat throughout its width, and additional strips of material l8lb and182b can be affixed along the edges thereof to provide the desiredraised portions.

What is claimed is:

1. In a measuring instrument of the type comprising a rotor, supportmeans, and taut band suspension means mounting the rotor on the supportmeans, the suspension means comprising two inner connector memberssecured to the rotor, two outer connector members secured to the supportmeans, each of the connector members presenting a convex supportsurface, and two thin resiliently flexible taut bands suspensionelements each extending across the convex support surfaces of adifferent cooperating pair of the inner and outer connector members, theend portions of the suspension elements being secured at points radiallyspaced from the axis of rotary movement established by the suspensionelements, the instrument further including cooperating stop means whichlimit outward movement of the outer connector members and axial movementof the rotor relative to the support with the outward movement of theouter connector members being held to less than the axial movementallowed the rotor, the improvement comprising two raised portionsprovided on the convex support surfaces of each of the outer connectormembers, said raised portions of each connector member extendinggenerally in the direction of the length of the suspension element andbeing spaced apart, transversely of the suspension element, by distanceat least about twice the width of the suspension element, the convexsupport surface of the respective connector member being smooth anduninterrupted between said raised portions; each suspension elementextending outwardly across the convex support surface of the respectiveconnector element in a location at least substantially centered betweensaid raised portions and thence radially away from the axis of rotationestablished by said suspension elements along a line which at leastapproximately intersects the axis of rotation and being secured, at apoint spaced radially from the axis of rotation, by a fused metal jointtending effectively to constrain the suspension element to its positionbetween said raised portions, the convex support surfaces of said innerconnector members being smooth and uninterrupted throughout the totalextent of said elements in directions transverse to the axis ofrotation. 2. A measuring instrument according to claim 1, wherein eachof said outer connector members comprises a resilient arm formed ofsheet stock and said raised portions are of rounded transverse crosssection and convex as viewed from the side of said support surfaceengaged by the suspension element. 3. A measuring instrument accordingto claim 1 wherein each of said outer connector members comprises aresilient arm formed of sheet stock and said raised portions areupturned edge portions of the arm. 4. A measuring instrument accordingto claim 1, wherein the length of said raised portions does notsubstantially exceed the limits, in the direction of the length of thesuspension element, of the respective convex support surface. 5. Ameasuring instrument according to claim 1, wherein the suspensionelements are flat bands of elongated rectangular transverse crosssection and the lateral space between said raised portions of each outerconnector member is such'as to allow the band, when engaged with therespective convex support surface, to shift laterally in eitherdirection, through a distance equal to 25-150 percent of the width ofthe band. 6. A measuring instrument according to claim 5, wherein thethickness of said bands is on the order of several ten thousandths of aninch and said raised portions project beyond the respective convexsupport surface by a distance equal to 1-10 times the thickness of theband in the area of the crest of the convex support surface.

7. A measuring instrument according to claim 2, wherein a locator notchis provided in each of said outer connector members at a point spacedfrom the convex support surface and the outer connector member includesa surface portion adjacent said notch, whereby in assembly thesuspension element can be stretched across the convex support surfaceand thence along the connector member and through said notch, and afused metal joint can then be established between the suspension elementand said surface portion while the suspension element is held in saidnotch and in taut condition.

8. A measuring instrument according to claim 1, wherein the suspensionelements are flat bands of elongated rectangular transverse crosssection, the thickness of the bands being on the order of several tenthousandths of an inch and the width thereof being several times thethickness; and the bands are secured to the outer connector members byspot welds having a dimension, in the direction of the length of theband, significantly larger than the width of the band, the bands beingbiased by said spot welds to assume positions substantially centeredbetween the respective raised portions even when the bands are slackenedas a result of impact on the meter.

1. In a measuring instrument of the type comprising a rotor, supportmeans, and taut band suspension means mounting the rotor on the supportmeans, the suspension means comprising two inner connector memberssecured to the rotor, two outer connector members secured to the supportmeans, each of the connector members presenting a convex supportsurface, and two thin resiliently flexible taut bands suspensionElements each extending across the convex support surfaces of adifferent cooperating pair of the inner and outer connector members, theend portions of the suspension elements being secured at points radiallyspaced from the axis of rotary movement established by the suspensionelements, the instrument further including cooperating stop means whichlimit outward movement of the outer connector members and axial movementof the rotor relative to the support with the outward movement of theouter connector members being held to less than the axial movementallowed the rotor, the improvement comprising two raised portionsprovided on the convex support surfaces of each of the outer connectormembers, said raised portions of each connector member extendinggenerally in the direction of the length of the suspension element andbeing spaced apart, transversely of the suspension element, by distanceat least about twice the width of the suspension element, the convexsupport surface of the respective connector member being smooth anduninterrupted between said raised portions; each suspension elementextending outwardly across the convex support surface of the respectiveconnector element in a location at least substantially centered betweensaid raised portions and thence radially away from the axis of rotationestablished by said suspension elements along a line which at leastapproximately intersects the axis of rotation and being secured, at apoint spaced radially from the axis of rotation, by a fused metal jointtending effectively to constrain the suspension element to its positionbetween said raised portions, the convex support surfaces of said innerconnector members being smooth and uninterrupted throughout the totalextent of said elements in directions transverse to the axis ofrotation.
 2. A measuring instrument according to claim 1, wherein eachof said outer connector members comprises a resilient arm formed ofsheet stock and said raised portions are of rounded transverse crosssection and convex as viewed from the side of said support surfaceengaged by the suspension element.
 3. A measuring instrument accordingto claim 1 wherein each of said outer connector members comprises aresilient arm formed of sheet stock and said raised portions areupturned edge portions of the arm.
 4. A measuring instrument accordingto claim 1, wherein the length of said raised portions does notsubstantially exceed the limits, in the direction of the length of thesuspension element, of the respective convex support surface.
 5. Ameasuring instrument according to claim 1, wherein the suspensionelements are flat bands of elongated rectangular transverse crosssection and the lateral space between said raised portions of each outerconnector member is such as to allow the band, when engaged with therespective convex support surface, to shift laterally in eitherdirection, through a distance equal to 25-150 percent of the width ofthe band.
 6. A measuring instrument according to claim 5, wherein thethickness of said bands is on the order of several ten thousandths of aninch and said raised portions project beyond the respective convexsupport surface by a distance equal to 1-10 times the thickness of theband in the area of the crest of the convex support surface.
 7. Ameasuring instrument according to claim 2, wherein a locator notch isprovided in each of said outer connector members at a point spaced fromthe convex support surface and the outer connector member includes asurface portion adjacent said notch, whereby in assembly the suspensionelement can be stretched across the convex support surface and thencealong the connector member and through said notch, and a fused metaljoint can then be established between the suspension element and saidsurface portion while the suspension element is held in said notch andin taut condition.
 8. A measuring instrument according to claim 1,Wherein the suspension elements are flat bands of elongated rectangulartransverse cross section, the thickness of the bands being on the orderof several ten thousandths of an inch and the width thereof beingseveral times the thickness; and the bands are secured to the outerconnector members by spot welds having a dimension, in the direction ofthe length of the band, significantly larger than the width of the band,the bands being biased by said spot welds to assume positionssubstantially centered between the respective raised portions even whenthe bands are slackened as a result of impact on the meter.